In situ combustion



Sept. 19, 1961 R. E.'KUNETKA 1N sITu coMBus'rIoN Filed July 1s, 195s United States Patent C 3,000,441 1N SITU COMBUSTION Robert E. Kunetka, Houston, Tex., assignor to Texaco Inc., a corporation of Delaware Filed July 18, 1958, Ser. No. 749,498 9 Claims. (Cl. 166-11) 'Ihis invention relates to the production of hydrocarbons, such as petroleum, from underground hydrocarboncontaining formations.

In situ the combustion has 'been proposed as a method of improving or enhancing the recovery of oil from underground formations. Explanatory of one type of an in situ combustion operation a high temperature zone is established in an oil-containing formation in the vicinity of a well bore penetrating the same. Suitable heating means 'for establishing a high temperature zone within the formation may comprise an electrical heating device or a gas fired bottom hole igniter or heater. A suitable device for initiating in situ combustion within a well bore is described in U.S. 2,722,278. Upon introducing a combustion supporting or an oxygen-containing gas, such as air, into the heated formation via the well bore a high temperature combustion zone is created by the reaction between the oxygen and combustible residues within the formation in the high temperature zone, such as com- -bustible residues resulting from the distillation and/or thermal cracking of oil or combustible material originally Iin place or introduced thereinto. Upon continued introduction of the combustion supporting gas this high temperature zone will commence to move into the formation outwardly from the well bore.

Leaving this high temperature zone is a relatively high temperature gas stream which, as it moves outwardly into the formation, loses `heat to the formation. By this method the high temperature combustion zone is moved for a considerable distance outwardly from the well bore without further direct application of heat to portions of the formation immediately surrounding the well bore. In some instances, however, continued direct application of heat to the lform-ation immediately surrounding the well bore may be desirable. The distance the high temperature combustion zone moves outwardly into the formation and as a result the volume of formation swept by or comprised within the in situ combustion zone, is determined by the relative magnitude of the rate of heat generation (combustion of combustible residues) `and the rate of heat loss to the surround-ing formation.

It has been postulated that the following mechanisms are important in this type of in situ combustion operation `for the movement of the high temperature combustion zone outwardly into the formation. Although the precise mechanism of an in situ combustion operation is not definitely known, the following sequence of events in an in situ combustion operation are postulated and are presented herein for the purpose of enabling one skilled in the art to better understand this invention.

As the high temperature combustion zone approaches any given volume of the hydrocarbon or petroleum-producing formation the temperature of this volume of formation rises. This results in a reduction in the viscosity of the -formation liquids due to temperature increase. 'Ihese liquids may then be moved more readily under the inuence of the stream of gaseous products of combustion continuously emanating from the high temperature combustion zone. As the temperature continues to rise, distillations of the formation liquids therein begin. The products of these distillations condense in cooler regions of the formation removed from the high temperature combustion zone. These distillations continue until the heavier components or hydrocarbons Within the formation begin to crack, yielding Ihydrocarbon gases and coke or similar carbonaceous residues. Also, as the temperature continues to rise and the oxygen content of the incoming combustion supporting gas increases due to depletion of combustible residues in preceding regions of the formation, a point will be reached at which the coke or other combustible residue will begin to react with the oxygen with the resulting release of heat to the formation and the on-moving combustion gas stream comprising gaseous products of combustion. This heat is carried away by the on-moving combustion gas stream and also to some extent by thermal conduction to adjoining regions of the formation. When the coke or combustible residues have been burned away there remains a volume of liquid-free formation which, unless otherwise treated, is gradually cooled by the relatively cool on-coming combustion supporting gas entering the formation via the well bore. It is mentioned that it is believed that the temperatures reached in the high temperature combustion zone are in the range 600- 2000 F., more or less, usually in the range 700-l500 F.

In laccordance with yet another type of an in situ combustion operation as completely described in U.S. 2,793,- 696 issued May 28, 1957, in the name of Richard A. Morse, after initiation of a high temperature combustion zone within a hydrocarbon-containing formation in the immediate vicinity of a well bore penetrating the formation, the supply of combustion supporting gas or air into the formation via this well bore is discontinued. Thereafter air or other suitable combustion supporting gas is introduced into the formation via another well bore spaced from the first mentioned well bore. The air thus-introduced into the `formation via this other spacedapart well bore serves to maintain the in situ combustion operation. However, in this instance the high temperature combustion zone moves in a direction countercurrcnt to the ow of air or combustion supporting gas through the formation. Moreover, in this type of in situ combustion operation, which may be conveniently called a reverse in situ combustion operation, all the displaced Iformation fluids pass through the high temperature combustion zone. In the first mentioned type of in situ combustion operation, which might be conveniently referred to as direct in situ combustion operation, the displaced hydrocarbons move -ahead of the in situ combustion zone and are not necessarily exposed to the high temperatures prevailing in the high temperature combustion zone.

It has been observed that the above-described reverse in situ combustion operation is useful for the displacement and recovery of relatively high gravity crude oils from formations containing the same, such as crude oils having a gravity above about 20 A.P.I., especially above 30 A.P.L Relatively low 4gravity crudes, such as crude oils having a gravity below about 20 A.P.I., are relatively less effectively displaced by the above-described reverse in situ combustion operation.

It is an object of this invention to provide an improved in situ combustion operation for the recovery of hydrocarbons, such as petroleum and the like, from a subsurfface Aformation containing the same.

It is another object of this invention to provide an improved method of carrying out an in situ combustion operation, employing the so-called reverse in situ combustion operation, which is particularly applicable for the recovery of viscous hydrocarbons from subsurface yformations.

Still another object of this invention is to provide a method of carrying out an in situ combustion operation generally applicable for the recovery of crude oil from relatively high gravity or relatively low gravity crude oil-containing formations.

How these and other objects of this invention are accomplished will .become apparent in the light of the accompanying disclosure made with reference to the accompanying drawing which schematically illustrates an embodiment of the practice of this invention,

In accordance with this invention a hydrocarbon-producing formation is penetrated'by a first well bore and by a second well bore, said second well bore being spaced apart within said formation from said first well bore. A high temperature Zone is then created in a Zone within formation adjacent said first well bore. This high temperature zone is then caused to be moved outwardly from said first well bore within said formation in the direction of said second well bore. Movement of this high temperature zone outwardly from the first well bore the formation in the direction of the second well bore is effected by the introduction of a combustion supporting gas, such as air, from said rst wel-l bore into said hydrocarbon-producing formation. While the thusin-itiated and maintained in situ combustion operation is canried out within the formation by the injection of a combustion supporting gas thereinto via said first well bore the resulting displaced formation uids, including formation hydrocarbons, are recovered from said formaf tion via said second well bore. After the resulting high temperature in situ combustion zone has been caused to move from the vicinity of said first well bore toward said second well bore for a substantial distance within said formation, the injection of air or combustion supporting gas into the formation via said first well bore is discontinued.

Thereupon an inert or non-combustion supporting gas is introduced into the formation via said first well bore. As this inert gas moves through the formation the thusin'uroduced inert gas picks up heat from the high temperature in situ combustion zone previously created within the formation and transfers heat to the adjacent portions of the formation removed from said high temperature combustion zone in the direction of ow of the inert gas through the formation toward the second well bore. When a suiicient amount of heat has beenv thus transferred to. other portions of the formation adjacent said high temperature combustion zone such that formation fluids and/oi normally viscous hydrocarbons therein eX- hibit a substantially reduced viscosity a combustion supporting gas, such as air, is introduced into the formation via said second well bore. Upon the commencement of the injection of the combustion supporting gas into the formation undergoing treatment the above-referred socalled reverse in Vsitu combustion operation takes place. Upon injection of the combustion supporting gas into the formation vila said second well bore the high temperature combustionzone still continues to move within the formation in the original direction, that is, from the first well bore toward the second Well bore but now countercurrent to the ow of the combustion supporting gasintroduced into the formation via said second well bore. During this spo-called reversein situ combustion operation the resulting displaced formation hydrocarbons are recovered from the formation via said first well bore. It is mentioned that the injection of the aforementioned inert or noncombusion supportinggas is continued for a sufficient period of time to heat the ladjacent forward portions of the formation sufliciently toreduce substantially the viscosity of the formation uids (oil) therein. Care, however, should be taken to avoid cooling the formation, particularly ythe high temperature combustion zone and adjacent regions within the formation below the ignition temperature or combustion temperature of the combustible materials therein, such as a temperature below about 500 F.

By operating in the aforementioned manner, which operations may be carried out alternately, a subsurface formation containing low gravity crudes, such as crude 4 oils having a gravity below 30 A.P.l., especially a gravity below 20 A.P'.I., can readily be produced.

Referring now to the accompanying drawing which schematically illustrates an embodiment of the practice of this invention directed to the production of oil from an oil-containing formation, as illustrated in the drawing 1an oil-containing formation 11 is penetrated by a first well bore 12 and by a second well bore l14, the second Well bore 14 being spaced-apart from said first well bore 12. In the initial operation of the practice of this invention gas or air permeability is established across formation 11 by the introduction of gas or air via the annular space in well bore 12 between casing 15 and production tubing 16 and through perforations 18 into formationll in `the direction of or for recovery at said second well bore 14 through perforations 19 and/ or perforations 20 therein. If desired, gas permeability may be established Within formation 111 by introducing gas or air into formation 11 via perforations 19, gas or air being supplied thereto via the annular space within well bore 14 between casing 21 and production tubing 22 therein. Following the establishment of gas or air permeability across formation 11 a high-temperature Zone is created by suitable means, such as by means of an electrical igniter or gas fired bottom igniter in the vicinity of well bore Y12 within formation 11. Following the establishment of this Ahigh temperature zone within formation 11 adjacent Wellbore 12 a combustion supporting gas, such as airgis introducedintothe annular space between casing 15 and production tubing 16 via perforations 18 into formation 1.1. This injected combustion supporting gas or air upon entering formation 11 via perforations 18 serves to maintain and/or initiate in situ combustion therein and to move the previously created high temperature zone, wherein in situ combustion now takes place, outwardly from well bore l1 2 within formation 11 in the direction lof well bore 14. During the injection of air through well bore 14 via perforations 18 into formation 1 1 to maintain in situ combustion therein, the resulting displaced formation fluids, including formation hydrocarbons, are recovered from formation 11 via perforations 20* located within casing 21 in the lower portion of Well bore 14. These displaced formation fluids are recoveredgat the surface via production tubing 22 within well bore 14.

Upon continued injection of combustion supporting gas or air via well bore 12 and perforations 18 into formation 11, and after the high temperature in situ combustion zone 24 has been moved outwardly from well bore 12 Within formation 11 in the direction of Well bore 12, the injection of air into formation 11 via well bore 12 is discontinued. Thereupon an inert or noncombustion supporting gas is introduced into formation 11 via the .annular space within well bore 12 between casing 15 and tubing 16 and perforations 18. The thusinjected inert or non-combustion supporting gas upon passing through formation 11 from Well bore 12 in the direction of Well bore 14 picks up heat from the previously burned out portion of formation 11 which has already undergone in situ combustion and from the high temperature combustion zone 24 therein and transfers this heat to other yportions of formation 11 adjacent and removed from high temperature zone 24 therein in the direction of well bore 14 and the ow of the resulting heated inert gas Within formation v11. As a result those portions of formation 11 not previously subjected to in situ combustion are now heated toa relatively elevated temperature, such as about ignition temperature, for the combustion hydrocarbons and/or the carbonaceous residue therein while at the same that portion of formation 11 previously swept by the in situ combustion zone is cooled. As a result of thus heating the other portions of formation 11 between the high temperature combustion zone 24 and well bore 14 the viscosity of the formationdluids therein, particularly liquid hydrocarbons or crude oil therein, is substantially reduced. Further, it is mentioned that during the injection of the inert Igas into formation 11 via well bore 12 and perforations 18 any resulting displaced formation uids or hydrocarbons are recovered from formation 11 via perforations 20 of well bore 14 and withdrawn to the surface by means of production tubing 22.

After a portion of the formation between high tem- -erature zone 24 and well bore 14 has been suitably heated to reduce the viscosity of the formation fluids therein and to bring the temperature of the combustible materials therein to at least ignition temperature or the temperature to which in situ combustion takes place, the supply of inert gas to formation 11 via -well bore 12 and perforations 18 is shut off. Thereupon combustion supporting gas or air is introduced into formation 11 via the annular space within well bore 14 between casing 21 and production tubing 22.

As this injected combustion supporting gas or air moves within formation 11 from well bore 14 in the direction of well bore 12 in situ combustion is initiated and/or again maintained formation 11, this time in the manner of the above-described, so-called reverse in situ combustion. As a result of the continued injection of combustion supporting gas into formation 11 via perforations 19 of well bore 14 the high temperature combustion zone 24 wherein in situ combustion is now maintained still continues to move in the direction of Well bore 14 as indicated by the arrow in the accompanying drawing and countercurrent to the ow of combustion supporting gas now being introduced into formation 11 via perforations 19 of Well bore 14 toward well bore 12. During this reverse type in situ combustion operation production of formation fluids from formation 11 via well bore 14 and perforations 20 and production tubing 22 is discontinued, the resulting displaced formation uids now being recovered from formation 11 via perforations 25 in the lower portion of well bore 12. As indicated in the accompanying drawing a packer 26 and a packer 28 are provided in the annular space within well bore 12 and well bore 14, respectively, to separate the injected uids and produced tluids, respectively.

In the practice of this invention any suitable inert or non-combustion supporting gas may be employed. Suitable non-combustion supporting gases include carbon dioxide, nitrogen, natural gas, gaseous products of combustion, particularly gaseous products of combustion produced during the in situ combustion operation and recovered from formation 11 by means not shown and rein jected into formation 11. The recycle of hot gaseous products of combustion from formation 11, recovered therefrom via perforations 20 of well bore 14 via tubing 22 and separated at the surface for reinjection, by means not illustrated, into formation 11 via perforations 18 of well bore 12, is particularly yadvantageous since these gaseous products of combustion are relatively hot and more readily induce high temperatures within those portions of formation 11 not yet swept by the high temperature combustion zone 24. By operating in the aboveindicated manner as illustrated in the drawing a hydrocarbon-producing formation, such as one containing a low gravity or highly viscous crude, is satisfactorily produced by the so-called reverse in situ combustion.

If desired, and/or if advantageous, the above-described operations employing direct and reverse in situ combustion in sequence may be alternately repeated. By alternately carrying out so-called direct and reverse in situ combustion operations for the recovery of petroleum from formation 11 the temperatures at the producing well can be controlled to avoid creating undue high temperatures therein since in each type of in situ combustion operation a different well bore is employed for producing the resulting displaced formation hydrocarbons. More particularly, when an in situ combustion operation is carried out within formation 11 the injection of combustion supporting gas .into formation 11 via perfortions 18 of well bore 12, the resulting displaced formation liuids are recovered from formation 11 via perforations 20 of well bore 14. In this operation well bore 14 serves as the producing well. When the formation temperature experienced at well bore 14 during this in situ combustion operation tends to become unduly high, reverse in situ combustionV is then carried out within formation 11 in the manner in accordance with this invention. When reverse in situ combustion is carried out within formation 11 well bore 12 becomes the producing 'well since the resulting displaced formation uids are recovered from formation 11 via perforations 25 of well bore 12.

As will be apparent to those skilled in the art in the light of the foregoing disclosure many modifications, alterations and changes are possible in the practice of this invention without departing from the spirit or scope thereof.

I claim: 1. A method of producing hydrocarbons from a subsurface hydrocarbon-producing formation containing heavy crude oil which comprises initiating in situ combustion in said formation in a zone adjacent a iirst well bore penetrating said formation, introducing a combustion supporting gas into said formation via said first -Well bore to maintain in situ combustion therein to make the more viscous crude oil less viscous, producing the resulting less viscous hydrocarbons from said formation via a second well bore penetrating said formation, discontinuing the injection of said combustion supporting gas into said formation via said first well -bore and injecting an inert gas into said formation via said rst well bore whereby heat from the high temperature in situ combustion zone within said formation is carried from said high temperature in situ combustion zone to another portion of the formation removed from said high temperature in situ combustion zone in the direction of said second well bore to reduce the viscosity of formation fluids, discontinuing the injection of said inert gas into said formation via said first well bore and introducing a combustion supporting gas into said formation via said second well bore to continue in situ combustion within said formation such that the high temperature in situ combustion zone moves within said formation in the direction of said second well bore counter-current to the flow of said combustion supporting gas introduced thereinto via said second well bore and producing the resulting less viscous hydrocarbons from said formation via said rst well bore.

2. A method in accordance with claim 1 wherein said combustion supporting gas alternately introduced into said formation via said iirst well bore and said second well bore to continue in situ combustion therein is air.

3. A method in accordance with claim l wherein said inert gas introduced into said formation via said rst Well bore has a heat transfer agent therein comprising gaseous products of combustion.

4. A method in accordance with claim 1 wherein the resulting displaced hydrocarbons are produced from said formation only via said rst well bore when combustion supporting gas is introduced into said formation via said second well bore.

5. A method in accordance with claim 1 wherein said inert gas introduced into said formation via said well bore is natural gas.

6. A method in accordance with claim 1 wherein said inert gas introduced into said formation via said first well -bore comprises methane enriched with normally liquid hydrocarbons.

7. A method of carrying out an in situ combustion operation for the production of hydrocarbons from an underground formation containing viscous crude oil having an API gravity less than 30 which comprises initiating in situ combustion within said formation in a zone adjacent a rst well bore penetrating said formation, introducnoone-41:

7 ing; air: into'said formation.` via saidrst weil.` bore-:td maintain-in situ combustion therein to reduce-the viscosity. of:v said crude oilv and to displace"V hydrocarbons of re; duced viscositysfrom `said `formation toward Va'sccond :well bore penetrating said` formation ati adistance removed from; said iirstV WeilY bore',l producing-vthevresultingj dis-v placed hydrocarbons yfrom :said formation via said :second well Y bore, .discontinuing the injectiongof-said combustion supporting gas into said formation viasaid first wellbore; introducing into saidformationv-viaisaidfiirst we11:bore a' non-combustion supporting; gas asi a' heatcarrier.I to trans#v ferthe heat'` from the high temperaturecombustioh zone createdrwithin said form'ationto anotherL portion-of said formation adjacent said high temperature combustionV zone in the direction of said second-well Vbore and-inthe direction of the ow of saidnon-combustionsilpporti'ng gas: Within said formation Ywhereby thel hydrocarbons: in said other portion. of the formationfarenheated to. a'relatively elevated' temperature to effect viscosity reduction;l discontinuing the injection of said non-combustiofspporting gas into Ysaid formationnviasaid rstwell-bore, introducing air into` said rformation-viaT said secondA Well bore. tol initiate vand/ormaintain. in situ combustion in thepresence .of hydrocarbons with reduced viscosity- Withinsaid formation in said otherportion of said-*formativn` un'der conditions suchthat'the-high-temperature combustionY zone Within said formation' resulting; from said inrsitu combustion moveswithimsaidv formation i11- the direction ofY said second Well-boreandhcountercur-Y rent to the flow of said combustion. supporting gas intro-- ducedinto saidrformation via'saidsecond well bore andproducing the resulting, displacednhydrocarbonsi ofV 1:e"Y dncedrviscosity from said formatiomvia: said-rst well bore.

8L A-'method in accordancewith c1aimv7 wherein said combustion supporting gas and non-combustion:support-A ing .gasintroduced into saidformation vvia said first Well bore are'aiternately injected intosaid. formation-With respectto the combustionsupportinggas introduced into said Yformation via said second well bore.

9. A method of.producinghydrocarbons'from an fundergr'ound formationcontainingfviscouscrudeoil having an @API gravityless than about 20.9 Whichcomprises 'estab-` lishing permeability withinr-saidf-formation between a rstwellfbore andi a-second We11-bore-penetratingsaid formation, said second wellborevbeingtremoved from said irstI well bore, creatingahigbtemperature combustion zone within said formation in a zone therein adjacent said rst-wellrbore,,introducingfair via said first Well bore into said formation to' initiate an'd/ or maintain in v situ combustion thereinVL and therebyreduce:t.1:|e-viscosityV of said viscous crude oilfin said formatiomproducing viafsaid second well bore hydrocarbons:ofvreducediviscosity` displaced from said' formation during in -situ combustion, discontinuing the injection of -a'ir -intoYsaid--formationvia said rst Well bore, introducing-.an inert gas-into-said formation'via saidrst wellzbore to transfer heat from the high temperature zone created within -said formation during the aforesaid in situ combustionloperation therein to heat an adjacentportion of. saidk formation removed from'said highl temperaturecombustion zonein therdirectionl ofi-flow of said inert gas therethrough toreduce the viscosity: of crude'oil in saidlforrnationwhile;continuingA the production` of displaced hydrocarbons 'and formation f uids via said secondV we1-1-bore,discontinuing theinjection of 'said inert gas into 4said formation avia said rst Well lbore; introducing air intosaid formation :via-.saidsecond well -bore to initiate 'inksitucombustionY within said formation in that portion thereof adjacent theaforesaidvhigh temperature combustionwzoneandvheated bythe ow of the aforesaid previously injected inert gas for reducing thevviscosity ofL crudeoil in Ysaid formation -therein and vproducing y,the resu1ting .disp1acedhydrocarbons from-saidiorrnation via said-irstwellbore- 

7. A METHOD OF CARRYING OUT AN IN SITU COMBUSTION OPERATION FOR THE PRODUCTION OF HYDROCARBONS FROM AN UNDERGROUND FORMATION CONTAINING VISCOUS CRUDE OIL HAVING AN API GRAVITY LESS THAN 30* WHICH COMPRISES INITIATING IN SITU COMBUSTION WITHIN SAID FORMATION IN A ZONE ADJACENT A FIRST WELL BORE PENETRATING SAID FORMATION, INTRODUCING AIR INTO SAID FORMATION VIA SAID FIRST WELL BORE TO MAINTAIN IN SITU COMBUSTION THEREIN TO REDUCE THE VISCOSITY OF SAID CRUDE OIL AND TO DISPLACE HYDROCARBONS OF REDUCED VISCOSITY FROM SAID FORMATION TOWARD A SECOND WELL BORE PENETRATING SAID FORMATION AT A DISTANCE REMOVED FROM SAID FIRST WELL BORE, PRODUCING THE RESULTING DISPLACED HYDROCARBONS FROM SAID FORMATION VIA SAID SECOND WELL BORE, DISCONTINUING THE INJECTION OF SAID COMBUSTION SUPPORTING GAS INTO SAID FORMATION VIA SAID FIRST WELL BORE, INTRODUCING INTO SAID FORMATION VIA SAID FIRST WELL BORE A NON-COMBUSTION SUPPORTING GAS AS A HEAT CARRIER TO TRANSFER THE HEAT FROM THE HIGH TEMPERATURE COMBUSTION ZONE CREATED WITHIN SAID FORMATION TO ANOTHER PORTION OF SAID FORMATION ADJACENT SAID HIGH TEMPERATURE COMBUSTION ZONE IN THE DIRECTION OF SAID SECOND WELL BORE AND IN THE DIRECTION OF THE FLOW OF SAID NON-COMBUSTION SUPPORTING GAS WITHIN SAID FORMATION WHEREBY THE HYDROCARBONS IN SAID OTHER PORTION OF THE FORMATION ARE HEATED TO A RELATIVELY ELEVATED TEMPERATURE TO EFFECT VISCOSITY REDUCTION, DISCONTINUING THE INJECTION OF SAID NON-COMBUSTION SUPPORTING GAS INTO SAID FORMATION VIA SAID FIRST WELL BORE, INTRODUCING AIR INTO SAID FORMATION VIA SAID SECOND WELL BORE TO INITIATE AND/OR MAINTAIN IN SITU COMBUSTION IN THE PRESENCE OF HYDROCARBONS WITH REDUCED VISCOSITY WITHIN SAID FORMATION IN SAID OTHER PORTION OF SAID FORMATION UNDER CONDITIONS SUCH THAT THE HIGH TEMPERATURE COMBUSTION ZONE WITHIN SAID FORMATION RESULTING FROM SAID IN SITU COMBUSTION MOVES WITHIN SAID FORMATION IN THE DIRECTION OF SAID SECOND WELL BORE AND COUNTERCURRENT TO THE FLOW OF SAID COMBUSTION SUPPORTING GAS INTRODUCED INTO SAID FORMATION VIA SAID SECOND WELL BORE AND PRODUCING THE RESULTING DISPLACED HYDROCARBONS OF REDUCED VISCOSITY FROM SAID FORMATION VIA SAID FIRST WELL BORE. 